A model of open economics composed of producers and speculators is investigated by numerical simulations. The capital flows from the environment to the producers and from them to the speculators. The price fluctuations are suppressed by the speculators. When the aggressivity of the speculators grows, there is a transition from the regime with almost sure profit to a very risky regime in which very small fraction of speculators have stable gain. The minimum of price fluctuations occurs close to the transition.